K2 Region Builder

K2 Region Builder is the whole point of the K2 Lab suite in one node: it replaces the long chain of K2 Region nodes with a visual editor. You press Edit layout, a detached window opens, you drag boxes onto a canvas, type a prompt and an identity prompt into each, attach any number of LoRAs per box with their own strength and routing mode - and it hands K2 Compose everything it needs: regions, loras, global_prompt, width, and height.

If you've used the standalone K2Lab desktop app from the Krea 2 regional-prompting scene, this is that workflow brought back into the graph. The author of this pack reimplemented it as nodes because that's the one thing K2Lab's own author explicitly wasn't going to do ("I don't like ComfyUI" is a direct quote from the K2Lab thread).

The editor window

The window is split 2/3 canvas, 1/3 inputs - regions list on top, details of the selection below. Draw on empty space to make a region, Ctrl-drag to stack one on top of an existing region, Alt-click to reach a box underneath. Eight handles resize; Fit spreads things out; the up-arrow in the list reorders, and order decides compile order. Esc closes. The Backdrop button pulls your latest render from the output folder behind the canvas so you can place boxes against a real composition, with a Dim slider to keep box edges readable.

The fiddly bits are handled for you. Overlapping regions are resolved by weighted picking - smallest box wins, so a full-canvas background box can never block a small subject box. And typing doesn't rebuild the panel, so you don't lose text-field focus on every keystroke.

The part other editors get wrong

Boxes are stored normalized (0..1) and rescaled shape-preserving whenever you change width or height: a square box stays square, its relative centre stays put, and if it no longer fits the canvas it shrinks evenly instead of being squashed. That's the difference between this and plain fraction-based editors like the Ideogram-4 prompt builder, where a 0.3×0.3 box silently becomes a wide rectangle when you switch 1:1 to 16:9. The conversion is reversible - 1:1 → 16:9 → 1:1 lands exactly back where you started.

The layout input is JSON (written by the editor, hidden in the UI) but you can paste a saved layout in by hand. global_prompt follows the same rule as everywhere in this suite: scene only, no people, or you get extra faces drawn in empty space.

Getting it running

Same install as the whole pack:

cd ComfyUI/custom_nodes
git clone https://github.com/ping1979ping/comfyui-FVMtools

Restart ComfyUI, find it under FVM Tools/K2. No extra Python dependencies - this suite only needs numpy. You'll still want the Krea 2 model files (Turbo or RAW transformer, Qwen3-VL encoder, Qwen-Image VAE) in place before you press Queue.

Wire regions + loras + global_prompt + width + height straight into K2 Compose, and you're one K2 Regional Sampler away from a two-character image with no crop compositing. If your boxes land wrong, run K2 Region Preview first - a bad layout is much cheaper to spot there than in a full render.